1. Field of the Invention
The present invention relates to multilayer laminates of polyolefins and thermoplastic polyesters. The invention laminates are particularly suited for the manufacture of pipes.
2. Discussion of the Background
Plastic pipes made of polyolefins, in particular polyethylene and polypropylene, are known and are used in many applications. To perform their tasks the pipes have to be, inter alia, inert to the medium flowing therein and resistant to high and low temperatures and to mechanical stressing.
Single-layer pipes of polyolefins are unsuitable for many applications. For example, polyolefins provide insufficient barrier action against fuels. This leads, because of increased environmental consciousness and corresponding strengthening of world-wide legal regulations, to single-layer polyolefin pipes used for the transport of fuels, for example in underground supply lines, having to be replaced by pipes having improved barrier action.
JP-A 51-92880, incorporated herein by reference, describes composites, pipes and hollow bodies made of a polyester layer and a polyolefin layer, in which these two layers are bonded via an intermediate layer of modified polyethylene which contains from 0.1 to 10 mol % of an unsaturated carboxylic acid or a derivative thereof. This intermediate layer can comprise copolymers of ethylene and methacrylic acid, ethylene and acrylic acid or ethylene and vinyl acetate. However, and as will be shown in the examples of this document, the layers of these reference composites can be mechanically separated from one another. There is clearly insufficient cohesive adhesion between layers.
It is therefore an object of the present invention to provide multilayer plastic laminates, particularly multilayer plastic pipes, based on polyolefins, in particular polyethylene, which, compared with single-layer pipes of polyolefins, have improved barrier action against (petro)chemical materials, in particular against methanol- containing fuels.
Another object of the present invention is to provide laminates, particularly multilayer pipes, wherein all adjacent layers are cohesively bonded to one another.